In the more advanced high speed pickers used in warehouse product distribution systems to pick and dispense hard-type packages containing products of many different kinds and in very high volumes of orders and product units, the pickers each have a storage and feed magazine located above a separately motor powered product dispensing mechanism. The packaged products are loaded in a stack in the magazine and the dispensing mechanism is selectively operated to timely pick and dispense the products from the bottom of the stack onto a passing high speed product gathering conveyor. A series of these pickers with different packaged products are located along one or both sides of the conveyor and are controlled by a computer which is inputed with work orders and independently operates the pickers to pick and dispense selected products in selected quantities onto the passing conveyor within a time logic window. The time logic window is variable and is adjusted by the computer to a time period just sufficient to accomplish the required picking tasks so as to minimize the picking time for the various orders. So it is imperative that the dispensing mechanisms be able to consistently perform their required tasks as anyone of them that is not performing in the prescribed manner could disrupt the operation of the entire system and cause shortages in the picking.
Dispensing mechanisms for both hard-type and soft-type packages are available in various forms as disclosed in U.S. Pat. Nos. 4,805,376; 5,064,341 and 5,271,703 and German Offenlegungsschrift DE 41 01 615 A 1. Those believed to produce the best dispensing action for relatively hard-type packages such as contemplated here have one or more chains or belts with cogs that travel linearly in their dispensing action and engage the lower edge of one side of the package at the bottom of the stack and propel it at the proper time off a stack supporting platform onto the passing conveyor. Such a dispensing mechanism with a single cogged chain is disclosed in the above U.S. Pat. No. 5,271,703 (see FIG. 5). In such mechanisms, the cogs have a blunt configuration and provided the adjacent packages in the stack do not tenaciously stick to each other, the swift cog engagement dispensing action that is required does not damage the package and the dispensing occurs in the required timely manner.
Efficient and accurate picker operation is of particular importance in the case of direct distribution systems providing variable client specified price labels where orderly high speed picking and conveyance through the system is required. An example of such a direct product distribution system adapted to process packaged videocassettes is disclosed in U.S. patent application Ser. No. (attorney's docket number P-301) entitled "Product Distribution System" filed concurrently herewith and assigned to the assignee of this invention. In such a system, the pickers are required to dispense the packaged videocassettes onto a high speed product gathering conveyor in an orderly spaced manner so that they may then be efficiently conveyed and processed for price labeling and packing.
In the packaging of videocassettes and other products where it is desired that the identifying box or case containing the product be sealed, it is common practice to cover the product container with a low cost shrink wrapped sheet or film of transparent poly vinyl chloride (PVC). This has been found to present a processing problem in dispensing which is most acute when the case for the product is a so-called "clam shell" that is also made of PVC. Due to heat, humidity, and the adhesive characteristics of PVC, the packages, and particularly those where the package is a vinyl clam shell, have a tendency to stick together with an adhesive strength that increases with increasing temperature and humidity. When this sticking becomes pronounced, it has been found that conventional dispensing mechanisms are no longer able to free the package from its stack quickly enough to effect the programmed spacing on the conveyor. Moreover, these conventional dispensing mechanisms can then damage the package and/or the product and may not even be capable of freeing the product package at all resulting in a jam up in the feed magazine and a shortage in the picking.
For example, the force required of the above mentioned dispensing cogs to overcome the adhesion between the packages can become so great as to cause the cogs to imprint the product package resulting in an item that must be replaced after having been received on the conveyor and processed through the system. In some instances, the resisting force can even be so great as to cause the cogs to impact the package so severely as to break a product such as a plastic videocassette case. Or the cogs may even tear through and across the underside of the package and not actually effecting its dispensing onto the conveyor and leaving the package mangled and possibly jammed in the stack on the dispenser. In an attempt to solve this problem, dry-type lubricants have been suggested for the PVC shrink wrap but they can possibly contaminate the dispensing mechanism and other apparatus in the distribution system. It has also been proposed to change the wrapping material to one that does not have such sticky characteristics but they have thus far been found to be more costly and may not be at the option of the management of the distribution system and with the choice dependent on who is in control of the packaging.